This invention relates to dental crowns for teeth, and particularly to pre-formed crowns, generally of cup-shaped, which are intended to be custom fit to the tooth of a patient during a single dental visit.
Advantages of the use of such pre-formed crowns, in contrast with crowns which are cast from a mold of the tooth to be crowned, are that the crowns can be inexpensively mass produced, can be of a material, such as annealed stainless steel, which is far less expensive than the noble metals commonly found in custom cast crowns, and can be permanently fitted in a single, continuous procedure.
A disadvantage of such pre-formed crowns, however, is that because they are shaped on site, generally using simple hand tools, the material of the crowns must be relatively easily workable. This, in turn, requires that the walls of the crowns be ductile and relatively thin, which gives rise to problems of strength and durability, especially on the occlusal or biting surfaces. Thus, while the use of pre-formed crowns is less expensive and more convenient than the use of custom cast crowns, such pre-formed crowns generally require much earlier replacement due to premature wear or perforation.